Only loop and check isAlive in MongoCursor.next() when cursor is tailable (#725)

Author: kmahar

Sources/MongoSwift/AsyncAwait/MongoCursor+AsyncSequence.swift

@@ -50,17 +50,25 @@ extension MongoCursor: AsyncSequence, AsyncIteratorProtocol {
      *   - `DecodingError` if an error occurs decoding the server's response to a `T`.
      */
     public func next() async throws -> T? {
-        while try await self.isAlive() {
-            if Task.isCancelled {
-                return nil
-            }
-            if let doc = try await self.tryNext() {
-                return doc
-            }
-            await Task.yield()
+        guard !Task.isCancelled else {
+            return nil
         }
 
-        return nil
+        switch self.cursorType {
+        case .nonTailable:
+            return try await self.next().get()
+        case .tailable, .tailableAwait:
+            while try await self.isAlive() {
+                if Task.isCancelled {
+                    return nil
+                }
+                if let doc = try await self.tryNext() {
+                    return doc
+                }
+                await Task.yield()
+            }
+            return nil
+        }
     }
 
     /**

Sources/MongoSwift/MongoCursor.swift

@@ -38,6 +38,8 @@ public class MongoCursor<T: Codable>: CursorProtocol {
 
     private let wrappedCursor: Cursor<MongocCursor>
 
+    internal let cursorType: MongoCursorType
+
     /// The `EventLoop` this `MongoCursor` is bound to.
     internal let eventLoop: EventLoop?
 
@@ -67,6 +69,7 @@ public class MongoCursor<T: Codable>: CursorProtocol {
         self.client = client
         self.decoder = decoder
         self.eventLoop = eventLoop
+        self.cursorType = cursorType ?? .nonTailable
 
         self.wrappedCursor = try Cursor(
             mongocCursor: MongocCursor(referencing: cursorPtr),